PEOGRESS OF METEOROLOGY IN 1889. 225 



ordinary pattern whose constants had also been determined. These 

 comparisons have shown that the wind velocities computed from the 

 ordinary anemometer average iO per cent, higlier than the wind ve- 

 locities given by the little anemometer having- very small inertia, and 

 that the percentage of excess increased with decrease of wind velocity. 

 An anemometer was then tried whose cups were weighted, and still 

 greater percentages of excess were discovered. {A^n. Meteor. Journal, 

 VI, p. 115.) 



The wind force committee of the Eoyal Meteorological Society, 

 consisting of Mr. G. M. Whipple and Mr. W. H. Dines, has made a 

 report on experiments with anemometers at Hersham. A whirling ap- 

 paratus of 29 feet radius was rotated by means of a small steam-engine. 

 On the arms of tne whirler four different anemometers were placed ; 

 each experiment lasted fifteen minutes, the steam-pressure remaining 

 constant during the run. For the new standard anemometer with arms 

 2 feet long the experimenrs gave a mean value for Eobinson's factor 

 of 2.15, and for two smaller instruments the factor is 2.51 and 2.9(3. Mr. 

 Dines' helicoid anemometer gave very satisfactory results, the mean 

 factor being 0.996. {Nature, xxxviii, p. 191.) 



Air pressure against moving plates. — The results of lieckniigers ex- 

 periments on the resistance of the air to the moliou of plates on a 

 whirliug-macliine agree in general with those of other experimenters. 

 He finds that the total resistance is greater the smaller the distance ot 

 the plate from the axis of rotation. The total resistance B which a 

 circular plate of diameter D experiences when rotated at a distance 

 L from the axis of rotation is from his experiments — 



in which i7 represents the pressure due to the velocity, or \y — . A for- 



mula is given for the distribution of pressure over the front of the 

 [)late, and the diminution of pressure behind the plate is shown to de- 

 pend largely on its diameter. { Meteor ologische Zeitschrift, 1889, vr., p. 3.) 

 Mr. W. H. Dines has conducted a series of whirling-machine experi- 

 ments to determine the prcissure on various shaped objects placed at 

 the end of the arm and whirling with difterent velocities. The machine 

 was operated by steam-power. Tne [)ressure upon a plane plate three- 

 eighths inch thick, and either round or square, was found to be 1.51 

 pounds per square foot for a velocity of 20.86 miles per hour. The 

 l)ressure upon the same area is increased by increasing the perimeter. 

 The pressure upon a one quarter- foot plate the author states to bo pro- 

 portionately less than upon a plate either one-half or double its size, 

 and the pressure upon any surface was found to bo but slightly altered 

 by a cone projecting at the back. [Qnar. Jour. Hoy. Met. 6'oc., XV, 

 p. 187.) 



H. Mis. 221 15 



